The present invention relates to an implant which engages a spinal column to hold a longitudinal member or rod in position relative to the spinal column.
Spinal implants have been used in treatment of patients with deformed and/or mechanically insufficient spinal columns. Longitudinal members or rods have been contoured to a desired configuration and connected with a spinal column. Among the various devices used to connect a rod with a spinal column have been hooks having through openings which receive the rod. While the hook is loose on the rod, a blade or free end of the hook is moved into engagement with the spinal column. Once the hook has been positioned relative to the spinal column, a set screw or clamp member is tightened to securely interconnect the hook and the rod.
In the past, difficulties have been encountered in positioning the hook and rod relative to the spinal column. If the hook is placed on the rod before being connected with the spinal column, the rod tends to interfere with placement of the hook relative to the spinal column. If the hook is connected with the spinal column before being positioned on the rod, difficulty may be encountered in moving the rod through an opening in the hook without disturbing the placement of the hook relative to the spinal column.
The concept of providing a top-entry opening in a hook to receive a rod without sliding the hook along the rod is disclosed in U.S. Pat. No. 4,269,178 issued May 26, 1981 and entitled "Hook Assembly For Engaging A Spinal Column". This patent teaches that the hook is to be held in place by the use of a sleeve and a locking nut. The locking nut engages external threads on the rod and must be threaded along the rod to a position where the hook is to be located. In addition, the sleeve must be positioned on the rod adjacent to the locking nut